The present invention relates to a new and improved method of, and apparatus for, melting in a bath of molten metal a melting stock which is composed of fractured or comminuted scrap metal and/or highly contaminated, slag-rich coarse scrap material.
The coarse scrap material, for example, constitutes dross or other scrap material which is comminuted in a mill. The term "dross" designates a type of slag which contains metal oxide, metal and other contaminants. This material floats to the surface of the melt in a melting furnace and is removed or scraped-off the melt at predetermined time intervals.
In order to process such scrap metal, particularly in order to recover the metal from this scrap material, it is known to melt-out the scrap material in a rotary kiln which contains a salt bath. A disadvantage of such method is the low efficiency of energy utilization and the burden it places on the environment. The thermal energy remaining in the flue gases of the flame burners which are used for heating cannot be directly further used in a recuperator because the flue gases contain aggressive components. The base salts which are required for the process in a proportion of about 30 percent of the molten metal must be melted conjointly with the scrap material which requires an additional expense of energy. The environment is burdened by the salt vapors which are formed while the method is carried out. A further detriment to the environment is the salt slag which is obtained after termination of the process and which has to be deposited at a waste dump location or has to be stored and regenerated using technically expensive processes.
Another method of processing scrap metal, particularly scrap material from non-ferrous metals as known, for example, from German Patent Publication No. 2,241,070, uses pocket or crucible melting furnaces in which the scrap material is melted by direct heating in a primary melting chamber. The scrap material to be melted is preferably pre-heated and slides along the bottom of the primary melting chamber. This bottom forms a slide and the scrap material thereon is pre-molten by the burning gases which exit from a burner and directly impinge on the scrap material. The material slides on the slide into a secondary melting chamber in which it is completely melted by means of the radiative heat of further burners.
The melting capacity of this arrangement is comparatively low in relation to the volume of the metal bath. It is a further disadvantage of the known process that high metal losses occur and that there is a tendency to form lumps or agglomerations due to oxidation during the melting operation in the open melting pocket.
Additionally, flux additives are required to liquify the slag and energy losses occur due to over-heating of the metal bath which can be prevented only with difficulty and due to radiation from the surface of the melting pocket.